I assume the one with the highest number but it makes no difference at all. I've used the same Asus DVD/CD burner in every build since about 2009. It's not like an optical drive will perform differently if it's rated at the same read and burn speeds. And it certainly won't make your computer faster.
I have to agree. I had a couple of them (back when 52x cd speeds were the cat's meow) and they only seemed to last a year or two. They were pretty loud, sounded like it was going to take off. I've used asus the past couple of builds, they're still a little loud but not as bad. They've lasted me a lot longer.
After looking at the product pages, I don't see any speed differences between the 324 and 124 so it doesn't seem to make much difference. The higher number is probably newer and might have to do with which firmware it's shipped with.